Activity Reports show null Target Name fields incorrectly for some Activities

While testing a custom Activity Report template extension, we noticed an issue where some Activity records in the report results would have a null Target Name field, even though the Activity does have a value for that field.

This was tested against the core Activity report in demo CiviCRM.

Steps to reproduce:

1. Create an Activity report with Target Name field included
2. Filter results by Target name is empty (null)
3. Click through to the Activity record (click on the Activity Type link) - Event Registration was used in the example
4. See Activity record should have a "With" contact value - in the case of Event Registrations, this is the Participant value, but check this value for whatever is appropriate for Contributions, Membership Signups, etc
5. Click through to contact and open their Activities tab
6. See Activity record in the list with the contact's name in the "With" column - not null

See attached screenshots from demo CiviCRM.